Research On Rain Water Catchments & Subsurface Seep-Irrigation Under Gravitational Pressure In Greenhouse

China, a big agricultural country, is one of the thirteen countries poor in water. The shortage in water resource will be one of the biggest handicaps to economic growth and it is necessary to look for the new technology in irrigation saving water and energy. A lot of research shows that rainwater harvesting and water saving irrigation technique can not only utilize rainfall most, but also be beneficial to improve the planting environment. Basic on the abundant rainfall and areas for greenhouse planting in middle and lower reaches of the Changjiang River, rainwater harvesting, laws of seepage flow in low hydraulic pressure, and using subsurface seep-irrigation under gravitational pressure in greenhouse were researched.First, experimental study on the technique of rainwater harvesting. For the sake of filling a vacancy in the technique of rainwater harvesting in test area, using the information of precipitation and water needed for planting and through one year's rainwater harvesting experiment, the results show that the average modulus of runoff was 0.8989, and the volume of harvesting water was 14.76 m3 in the greenhouse with 13.44 m~2 superficial area. Based on these, the coupling between harvesting-water and water needed for planting was analyzed. The water between harvest and consume was balanceable for two and three batches planting one year except from July to September for three batches.Second, some experimental study on the technique parameters of designing seep-irrigation under gravitational pressure. From a series of contrastive experiments in different conditions of seep-irrigation, laws of infiltration rate, infiltration capacity, soil moisture migrating and distributing were analyzed. In air, the equation coupled between infiltration capacity and time was Q=12.5343t~0.6827( R~2=0.967), and between infiltration rate and time the equation coupled was V=3.9926-0.007t+7.1×10~-6t~2—2.0×10~-9t~3 (R~2 = 0.997); in soil, the equation were Q = 5.6344t~0.8402(R~2 = 0.999), and V = 3.2447-0.0048t+6.1×10~-6t~2-3.0×10~-9t~3(R~2=0.995). Cubic equation (R~2=0.988) of curvilinear regression between wetting front migration and time was more suited than Quadratic equation. The higher in hydraulic pressure, the quicker in rate of wetting front migration towards all directions. When soil moisture was higher and soil compaction was lower, rate of wetting front migration downwards was more and more quick, but the rate upwards less and less. In the course of seep-irrigation, the curvilinear of soil moisture took on figure with three waves. The biggest wave lied in around the seepage-pipe, near it were the two smaller waves. When seep-irrigation going on, the value of the big wave was steady-going and the two smaller was migrating forwards, then the area of wetting turned larger and soil moisture turned higher. After irrigation, the area of wetting and thevalue of soil moisture were influenced by hydraulic pressure, initial soil moisture, and soil compaction. In the experiment on hydraulic pressure and irrigation uniformity, the curvilinear regression between them was q= 2.018h1324(R2=0.937). To unchangeable hydraulic pressure level, irrigation uniformity of seepage-pipe per meter was increasing with the hydraulic pressure lowering. Under 80cm hydraulic pressure and more lower, irrigation uniformity of seep-irrigation was more than 0.87. To changeable hydraulic pressure level, irrigation uniformity was not change a lot, and the value was between the irrigation uniformity to the utmost pointsThird, the practical effect of the system. Based on above experiments, the system of rainwater harvesting and seep-irrigation under gravitational pressure was used in planting in greenhouse. By the environmental factors and vegetable growth status in three mouths, following results were gained: average air relative humidity was descended 8.5% in fine day, 6.5% in cloudy day, average air temperature was ascended 1°C~3°C, and soil temperature in 20cm depth subsurface was ascended 0.64 "C . The total volume seep-irrigation norm was 40% of that of pour-irrigation, and the average height of full-grown vegetable under SI was 4.3cm higher than that under PI.From above all, theory, experiment and practice were well integrated in this thesis. The end products not only can provide experience and technique parameters for rainwater harvesting and subsurface seep-irrigation under gravitational pressure in greenhouse, but also has great theoretical and practical significance in the development of water and energy saving irrigation in middle and lower reaches of the Changjiang River.